3D Robotics

 

This may be the most amazing thing we've ever posted here. DIY Drones member Brad Hughey built an electric multicopter capable of carrying a person (him), and then actually tried to fly it in his driveway (without a helmet!). Let's just say it didn't end well. But he's figured out what went wrong and he's going to give it another go.

 

In an email to me, he explains:

History was indeed made on August 10th, 2011 when the Revelation PoC prototype crashed unceremoniously in my driveway.  It did briefly leave contact with the Earth, and one could argue that you have to fly in order to crash, but I do not have the audacity to declare a success out of this debacle.  A root cause analysis has determined that multiple Magically Obliterating Smoke and Fire Emitting Transistor (MOSFET) failures are to blame.  If you listen real closely, you can hear the power rail line inductance ringing (a bit of electronics levity).  I wasn't laughing at the time, but an important lesson is finally learned; MOSFETs fail shorted (full throttle).  One failure in the back started the pitch forward, then three in the front failed, catapulting me down the drive perilously close to a parked car, missing a rotor strike by mere inches.

 

The resolution isn't great due to the use of USB instead of FireWire to copy it off of the camcorder.  That said, I'd rather this didn't go "viral", as it is a bit embarrassing.  Such is the nature of invention.  I proffer it mainly as a veracity enhancer; this effort is real and very close to success.

 

It is interesting to note that half the array out of ground effect managed to push the whole craft with me in it dragging against the asphalt for almost 20 feet before I managed to shut everything off.  The power is certainly there.  It's all a matter of control now, and the first thing to do next is make the power MOSFET stage for each thrust unit "bullet-proof".

 

The damage isn't as bad as it looks.  The real work involves a total redesign of the power stage including FUSES for each thrust unit.  There are much better MOSFETs around now, considering this iteration is seven years old. 

New changes frantically being applied include:

  • Higher current and more modern MOSFET devices
  • A resistor-capacitor snubber network across every MOSFET to help mitigate ringing overvoltages
  • Transient voltage suppressors (zener diode-based technology) across every MOSFET
  • A complete rewiring to minimize power rail inductance
  • FUSES on each motor as a fail-safe
  • Larger decoupling capacitors on the outrigger thrust units

We're a couple weeks away from another run at it. 

Yours in Daring Invention Progress,

 

Brad

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Comments

  • what i don't understand, when you use an Ardupilot type of stabilization, why didn't the front rotors slow down then the aircraft when it started to roll backwards?

  • It's a very interesting project and I wish you success in the next attempt.  It may be too complex if you mean to put it into commercial production. Tethering the aircraft for initial testing might be a good idea as suggested elsewhere. Since you designed and built the craft I agree you're probably the most qualifed to test flight it but the FAA would probably disagree. Since it's a rotorcraft you really need a rotorcraft rating even for an experimental AC: PPSEL is for fixed wing (you didn't mention any additional ratings).

  • i think you are wrong about the ground effect. it didn't happen here. what i think happened from the video is simple. the uplift force was high enough to lift you off the ground, then the MOSFET failure happened, the force vector of the vehicle was taken out of the vertical axis, while there was still uplift force the friction of the vehicle towards the ground was very low while the force vector was moving to the horizontal axis. so it's just logical that you vehicle was dragged over the ground backwards. there was no ground effect here.

     

    ground effect only applies to flying vehicles close to the ground. a bit like when you blow under a sheet of paper and it starts moving.

  • Unless with well simulation and safety backup (like at least an helmet) . I won't try like this cause life don't have 2nd chance.

  • awesome project, electric helicopters are just the next logic step with battery technology getting smaller and lighter. I'm sure there are a lot of projects behind closed doors in that direction. nice to see a hobbyist at the forefront of it.

     

    just one advise: wear a suit when test flying just like Igor Sikorsky did.

     

    curious, why don't you build a design with less but stronger motors? Do small motor have a better weight/lift ratio? would a frame based on some big bastards like this work and what are the ups and downs of bigger motors in a project like this?

     

    http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=...

  • Brad, very impressive. Glad you or someone else didn't get hurt! Do you have an online project log or any online resource documenting your adventure? Very interested in following what you are doing, seeing further successes and pouring over any other specs you feel like posting. Thanks!

  • Greetings again.

    @everyone_taking_about_sandbags: I confess that part of the mission here is the achievement of the first manned electric VTOL aircraft flight.  The danger is a bit over-stated, as no significant altitude or groundspeed is to be attempted.  The root cause of the "sticking throttle" problem shall NEVER happen again, and arguably, should never have happened in the first place.

    @Tom in ON: I question the true efficacy of autorotation as a fail-safe in typical flight modes (i.e. low and slow), as many a Robinson R22 pilot and V-22 proponent can attest, but the idea here is a highly available lifting platform through the use of redundancy.  There should be no single points of failure, and there won't be.  My ultimate answer to the parochial autorotation critics will be the incorporation of a Ballistic Recovery System chute as a fail-safe.  No other rotary wing craft can incorporate such a device.  Oh, and after watching the Sikorsky early test videos, I DO need wider landing gear.

    @Martin Szymanski: You're correct that mitigation of supply rail inductance is at the root of the failure issue, so I'm increasing the wire size and rerouting.  I have 3900mF lytics at the FETs now to help shunt some of the ringing, and at the longest runs I'm upping it to 10K.  Adding ferrites methinks would exacerbate the parasitic inductance problem, although I do have them in combination with some rather expensive metal film capacitors at the motor brushes to help suppress commutation noise.

    @Jack Crossfire: The MOSFETs failed because I did not properly apply them.  Mea culpa, and I don't have access to a DSO or EMC EMI/RFI testing facility capable of capturing aperiodic noise events.  So a bit of using The Force and best design practice art will fix it.  Ultimately, I believe you're correct about the brushless "DC" motors but I beg to differ on the propeller choice.  There are a myriad of definite aerodynamic differences between a model airplane propeller and a VTOL aircraft rotor, especially at the Reynolds number ranges in question.  A thorough discussion of static thrust in extreme ground effect is the stuff of which PhD theses are made.  We can take this discussion offline, if you like, or make a different thread.

    @Everyone_else: Thank you very much for your feedback and support.

     

  • Maybe it is time to consider using a geared down 2 stroke motor
  • 10/10 FOR CREATIVENESS. Guess he still has some PID's to set!! lol
  • Sounds like a lot of unnecessary engineering.  Manned, electric planes fly all the time, with brushless motors.  Just use a ton of ESC's, brushless motors, & GWS propellers & be done with it.  The back EMF, brush wear, & inefficiency of what you're trying to do is going to kill you.  You're going to have MOSFETs blowing up all the time & motors suddenly failing.  The sustained power output & RPM of flight is a lot higher than what cordless drills & battle bots have to handle.

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